1. Field of the Invention
The present invention relates to an inkjet type printing apparatus and an inkjet type printing method.
2. Description of the Related Art
An inkjet type printing apparatus ejects fine ink droplets from many nozzles formed in a printing head toward a print medium and shifts the printing head in a width direction (main scanning direction) of the print medium to print an image on a given surface of the print medium. When in this inkjet type printing apparatus, an ejection velocity of the ink droplet ejected from each of the nozzles in the printing head shifting in the main scan direction varies, a deviation in an arrival spot of the ink droplet occurs. The deviation in the arrival spot of the ink droplet causes disturbance in a print image. Therefore, it is required to maintain the ejection velocity of the ink droplet ejected from the nozzle to be constant.
Generally when a variation in an environment temperature or a temperature of the printing head creates a variation in viscosity of ink, an ejection velocity of the ink droplet, an ink ejection amount and a particle diameter of the ink droplet vary. When a head temperature of the printing head increases during printing to lower the ink viscosity, the ejection velocity of the ink droplet increases. The image has a possibility of blurring or being rough due to the variation in the arrival spot of the ink.
In addition, a variation in individual dimension or temperature characteristics of components constituting a printing apparatus body and a substrate, a variation in dimension of the nozzle or an ink flow passage of the printing head, a variation in sheet resistance of a heater or the like is one of the causes generating a variation in ejection velocity of the ink droplet for each apparatus.
Further, when an ejection characteristic of ink changes with a use state of the printing apparatus, the ejection velocity of the ink droplet possibly changes.
For example, Japanese Patent Laid-Open No. 2006-142806 discloses a technology of controlling the ejection velocity of the ink droplet to be constant by velocity feedback or temperature feedback. According to this publication, an optimum driving condition for ejecting the ink droplet is selected from a relation between the ejection velocity of the ink droplet and the temperature of the printing head to restrict a variation in ejection velocity of the ink droplet due to a variation in temperature of the printing head.
Incidentally in the technology disclosed in the above publication, variations in dimension of the power source and the substrate of each printing apparatus body, in heater resistance of the printing head and so forth are not taken into account. Further, in some cases, a value of the temperature of the printing head to be detected is not necessarily equal to a temperature in the vicinity of the nozzle during printing and the ejection velocity varies. The ejection velocity of the ink droplet can not be possibly controlled appropriately depending on the kind of the ink or a difference in use method of the printing apparatus.
The present invention has an object of providing an inkjet type printing apparatus and an inkjet type printing method which can restrict a fluctuation in ejection velocity of an ink droplet due to a temperature change of a printing head or variations in dimension of components constituting a printing apparatus body or the like to restrict degradation of an image.